I should be able to answer this question a lot better than I can since I have a degree in History of Art and Architecture… but if you don't use it, you lose it I guess. I'll give it a shot.

Mies van der Roe was an architect that first successfully pushed through this idea of using materials that create the building as also what makes the building beautiful. This expanded on the idea that form follows function.

Previous styles would put the form, beauty of the creation above if not equal to the function. This added a lot of "fluff". But once buildings moved from craft-type construction to industrial-type construction, it started to become clear that a new approach to beauty was needed. This was especially evident as cities became larger and sky scrapers became taller and more frequent.

Mies tried to find the beauty of industrial-type construction while also following the "form follows function" tenant. What followed ended up being extremely cost efficient because he used the structural materials to provide beauty, leaving out the costs from adding more material simply for aesthetics. As Mies always said, "God is in the details" so those who copied him didn't always get it right for their lack of attention to detail.

This was a significant impact towards the minimalist movement, which in turn influenced brutalism. Another big factor for brutalism is WWII and the politics around it. There was a lot of concern, "What about the little guy? How can we give the average Joe a quality of life?" To do so meant to cut costs. This thought process began in earnest after WWI, but it was after WWII and the rebuilding of Europe that it really came into fruition. There was a lot of thinking about the good of the collective, as evidenced by the architecture and prominent politics at the time.

Mies' minimalism starts taking off in the affluent rich cities while municipalities start thinking about how to house its people and the services they require, all on a budget. The big difference between minimalism and brutalism is the aesthetic "weight" of the building. This is due more to the materials chosen than intention (steel vs concrete), but the underlying thought process between the two can still be evident in the designs.

Minimalism strives to work with the materials and the environment, like sky scrapers appearing light. Brutalism is thinking more about how to provide to the people and be a symbol to the people, be it community or education or government's benevolence or what have you. Brutalism wants to be seen for the sake of being seen, while being cheap. Minimalism wants you to just get your desired task done without being in the way, physically and emotionally.

Brutalism had a push back against it's style due to the very fact that it didn't consider it's context and try to work with it. There was no God in the details. It timed itself so quickly as being part of the past, and as people recovered from WWII they just didn't want to be reminded of how poor and needy they were to demand such cheap construction and design. Politics began to be less all-important and brutalism stood as a reminder of the war sparked by severe sense of collectivism. It didn't have much to stand on it's own.

The "heavy" feeling most brutalist buildings turned the positive symbolism the building strived to be into its opposite. The "benevolent" government became oppressive. The "community" became "the poor people."

I hope I helped give some insight on this.

Firstly, your use of the term 'more artistic' is misinformed. Brutalism and Art Nouveau are both design movements - equally 'artistic' - and incidentally from the same overall intellectual project of European Modernism.

Modernism was a rejection of Classicism as the 'highest' form of architecture, art, and design. It was a revolutionary cultural movement, that arose with other great changes in European society. Amongst these was the Romantic ideal of individual genius, and the idea of scientific, intellectual, political and urban design progress, that became dominant during the European Enlightenment period.

Although Art Nouveau appears more 'decorative' or 'beautiful' to us now than Brutalism, at the time it was deeply shocking and revolutionary to a conservative audience. Its designs allowed for individual creativity and invention, which was not expected of classical designers or architects.

One of the core features of Modernism was the idea that these creative shocks were not merely to shock - but they were logical developments towards a better future. This was generally thought of as a cleaner, cheaper, safer, and more equitable society.

These ideas were most famously expounded by the Bauhaus school in Germany. Put simply, some of the core ideas of this school was the use of new materials, such as improved concrete, steel, and glass construction methods. These materials were seen as beautiful in themselves, and not requiring ornamentation. Form should follow function, meaning the lines of a building should be dictated by the needs of the building's occupants (rather than occupants changing their behaviour to suit a traditional building style). Just about every modern building, home appliance, and in particular Apple products (like the iPhone) show strong Bauhaus influences.

Brutalism was a particularly extreme form of Modernist principles. Particularly after the devastation of WWII, it allowed cities to be rebuilt quickly, and in a Modern, then hopeful, style.

As a side note, the design and aesthetic genius of key Brutalist structures have been re-recognized in the last decade or two, particularly in Britain. We are at an important point where this is not widely appreciated yet, and we are at risk of pulling down important parts of our architectural heritage and history. If you go to London, visit the Barbican centre, especially the water garden, roof garden, art galleries, schools and theatres - a Brutalist everyday utopia which is a great cultural achievement we might one day return to.